While liquefied hydrogen has a high energy density, it is an extremely low-temperature fuel (having a boiling point of 20.3 K at the atmosphere pressure), which results in a property of easily evaporating under the influence of the external environment (temperature difference, heat input from sunlight, etc.). Thus, storing such a fuel for a long period of time may lead to a decrease in the usable amount corresponding to the amount of evaporation, even if a large amount of the fuel has been initially stored. For a rocket used to launch a satellite or the like in which the fuel may be ignited again some time after the launch, in particular, a measure for reducing evaporation until the next ignition is required. As such a measure, one may consider reducing heat input from e.g. radiation heat from sunlight by covering the surface of the body of the rocket with a foaming heat insulating material. However, this measure alone may not be possible to reduce the amount of evaporation gas over a longtime storage by itself, because of the limit for reducing the amount of heat input from radiation heat.
Patent Document 1 discloses a storage tank that stores liquefied fluid for reducing generation of evaporation gas. The storage tank has a partition wall being a double wall between which a vacuum heat insulating space is formed, so as to shut heat penetration and reduce the amount of evaporation gas. Further, a liquid phase and a solid phase of the liquefied fuel are formed in a storage space, so that heat penetrating into the storage space is absorbed by melting heat of the solid phase, and heat input to the liquid phase is prevented to reduce the amount of evaporation gas.